1. Field of the Invention
This invention is directed generally to a coordinate detecting device employing a plurality of infra-red light beams, and particularly to such a device having a specially designed data processing circuit in order to reduce erroneous determination of the coordinates.
2. Description of the Prior Art
A touch panel system employing a plurality of light beams is well-known and described in U.S. Pat. Nos. 3,764,813, 3,775,560, etc. Such a touch panel system generally consists of a coordinate detection device and a display device, and forms a man-machine interface for any kind of computer system.
Specifically, as described in the above-mentioned U.S. patents, a plurality of light emitting diodes (LED) linearly arranged on a printed circuit board located on the left side of the display screen of a display device, such as a cathode ray tube (CRT), emit infra-red light beams which are received by a plurality of photo-transistors linearly arranged on a printed circuit board located on the right side of the display screen. At the same time, a plurality of light emitting diodes (LED) linearly arranged on a printed circuit board located on the bottom side of the display screen emit infra-red light beams which are received by a plurality of photo-transistors linearly arranged on a printed circuit board located on the top side of the display screen, thereby forming a grid of the infra-red light beams. Each of the LED and photo-transistor pairs is assigned a different address.
It can be known which of the LEDs emits the light beam and which of the photo-transistors on the opposite side detects the light beam by sequentially specifying the address to change the respective LEDs and the photo-transistors coupled therewith to form the pairs. A touch on the display screen with a finger or a pen causes interruption of a certain infra-red light beam. The X and Y coordinates at a location where the light beam is interrupted are transferred to a host computer to determine the touched position. The touch panel system is constructed such that the light beam is interrupted by a touch on the optical grid plane formed of the infra-red beams so that the sensing plane (optical grid plane) is made even.
Since the above-mentioned conventional optical touch panel device has an even sensing plane, if it is combined with a CRT having a curved display surface, a defect is encountered in that parallax is caused in peripheral portions of the CRT. For this reason, instructions for input data cannot be displayed on the CRT in a fine manner. Also, there is a fear of malfunction. Such parallax is caused by the fact that the infra-red light beams extend in straight lines over the curved display screen of the CRT. In other words, the infra-red light beams pass near the display screen at its central portion but far from the display screen in the vicinity of the edges thereof. Therefore, even if the operator touches a point near an edge of the display screen, parallax makes it difficult to interrupt the infra-red light beam corresponding to the desired point to be touched.
A touch panel device which can overcome the above-mentioned defects has been proposed by a copending U.S. application No. 300,333, filed Jan. 23, 1989, assigned to the present assignee.
However, even if the parallax problem can be solved, there remains various problems of providing a touch panel system free of malfunctions.
For example, assume that an operator touches an image (not shown) representing a command or the like displayed on the screen of a display apparatus by a finger (forefinger). If the other fingers are not adequately bent, one of them (for example, the thumb or the middle finger) may interrupt one of the infra-red beams at its tip.
In a conventional touch panel system in which the sensing plane is formed by infra-red beams orthogonally arranged in front of a rectangular screen, if the beams for detecting and determining the touched position in the vertical (up and down) direction (V direction) are sequentially emitted from the top side (in other words, carrying out the scanning from the top side to the bottom side), an infra-red beam is interrupted by the tip of the forefinger directing to the screen from the bottom side of the screen, whereby the touched position is determined by the first interrupted infrared beam.
However, as to the beams for detecting and determining a touched position in the horizontal (left and right) direction (H direction), the beam may be interrupted by the thumb on the left side of the forefinger or the middle finger on the right side of the forefinger (the positional relationship of the fingers is opposite if the operator touches the screen with the left hand) prior to the forefinger, depending on the scanning direction, that is, from left to right or from right to left, of the touch panel system, whereby a different position is erroneously determined as the desired touched position by the conventional touch panel system.
As described above, such a conventional touch panel system in which the sensing plane is formed by infra-red beams orthogonally arranged in front of its rectangular screen can possibly malfunction due to a hand of the operator which specifies a coordinate point on the touch panel.